4XE - Worse mileage than other motors (after battery depleted)?

[ormandj]

When researching the Jeep Wrangler 4xe before ordering, I very quickly noticed how every review (including Car & Driver’s July 2021 4xe Review) pointed out how the hybrid 4xe powertrain yielded a lower estimated “combined” fuel mileage than its gasoline counterparts. My curiosity got the best of me, so as I started researching the details of the 4xe powertrain and the details of how the EPA Fuel Economy estimate is determined, I learned some interesting things. I found Car & Driver's August 2020 article about Tesla EPA Range very informational and helpful.

How can a vehicle with an advanced hybrid powertrain achieve a lower "combined" EPA Fuel Economy score compared to its sibling that has the same shape, the same turbocharged 4-cyl engine, and albeit the hybrid portion, the same transmission, transfer case, & axles?

What I found is that most of the EPA Fuel Economy numbers are generated by the OEM’s, with only 15% of vehicles being actually tested/verified by the EPA. Vehicles are tested on a stationary dyno per a standardized set of city and highway test circuits, and the resistance force applied to the vehicle’s wheels from the dyno (road load) is determined from coastdown testing by the OEM to determine the vehicle’s rolling resistance, drag, and driveline losses.

Here are some of my observations:

• As others have noted, the Hybrid 4xe weighs more due to the EV battery and other additional powertrain components. This would add to the rolling resistance compared to the standard Wrangler. Will also require more force to accelerate the vehicle (but this extra energy should be recaptured when regenerative braking), not sure how this extra mass is accounted for when calibrating the resistance force of the dyno.
• I'd be curious how the vehicle dyno handles regenerative braking. This should greatly improve the city circuit of the test, unless the dyno doesn’t do a very good job of simulating the vehicle's inertia. Only the combined fuel economy score in Hybrid mode is published, would be curious what the individual City & Highway numbers are.
• The hybrid shouldn’t have much benefit during the highway test when running on gasoline, unless it allows the transmission to shift to a higher cruising gear than normal. If anything the added weight of the vehicle would make this test worse than a standard Wrangler due to higher “road load”.

We will use our Wrangler 4xe mostly for short trips within the electric range, so we are very happy with how the vehicle performs.

There are always losses involved in any transmission (small at these wire lengths) and any conversion, be it voltage or electrical to mechanical, generally in the form of heat. Regenerative braking doesn't recapture all of the expenditure on acceleration.

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[ND_4XE]

There are always losses involved in any transmission (small at these wire lengths) and any conversion, be it voltage or electrical to mechanical, generally in the form of heat. Regenerative braking doesn't recapture all of the expenditure on acceleration.

True about the losses with regenerative braking, but is a whole lot more efficient than a brake pad!

 

[ormandj]

True about the losses with regenerative braking, but is a whole lot more efficient than a brake pad!

Makes brake maintenance a heck of a lot less expensive, too. My heavy Volvo XC90 T8 is on the original pads and rotors at 60,000 miles. Eyeball 2.0 measurement shows about 3/4 pad life left, too.

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